One commercial defoliant product containing thidiazuron and diuron is sold under the tradename Ginstar by Bayer CropScience. This product is typically used for applying to cotton plants in an attempt to cause the leaves to fall off before the cotton is collected. Defoliants are often used to control plant growth. In the harvesting of cotton, defoliants are often applied to the cotton plants to cause the leaves to drop without adversely affecting the cotton boll. In this manner, the cotton can be harvested by machinery without contaminating the cotton with the leaves from the plant.
The activity of thidiazuron in the Ginstar product is believed to be due to the solvents used to disperse and spray the active ingredients. Numerous researchers have attempted to combine two active ingredients together at the same concentration. The results have not been able to obtain the same activity as thidiazuron alone or the product sold under the tradename Ginstar. Thidiazuron is very insoluble in many solvents, and thus, requires a mixture of exotic and expensive organic solvents and cosolvents. It is believed that these organic solvents contribute to the activity of the thidiazuron and its effectiveness as a defoliant. Ginstar is an emulsion concentrate containing 1-octyl-2-pyrrolidone and 1-dodecyl-2-pyrrolidone as essential solvents for producing the emulsion concentrate. The emulsion concentrate is mixed with water and applied to the plants as an emulsion. The organic solvents of Ginstar are highly toxic and dangerous to handle. The organic solvents are also believed to contribute to the sticky nature of Ginstar.
The Ginstar product has a disadvantage of producing a quick burn when applied to cotton leaves caused by the organic solvents. This causes the leaves to exhibit phytotoxicity that promotes the leaves to remain stuck on the plant rather than drop to the ground quickly. The solvents are believed to prevent the middle lamella from being fully dissolved, thereby preventing the leaves from falling quickly. A longer period of time is required for the leaves to fall from the plant naturally by gravity, wind and the like, since the desiccated leaves are not as heavy as non-desiccated leaves. The leaves that remain on the cotton plant are then incorporated into the harvested cotton and are processed during the ginning process. The small bits of leaves are then incorporated in the finished product and lower the quality of the cotton lint for the production of cotton goods such as clothes.
The action of thidiazuron affects the middle lamella of the cotton stem and dissolves the stem over a few days. This weakens the stem so that the leaves fall free from the plant thereby avoiding the problem of leaves being stuck to the plant and the quality issue as a result of the leaves remaining on the plant. The thidiazuron of Ginstar is sold as a stand alone defoliant. The thidiazuron is used at rates of 0.05 to 0.01 lbs. active ingredient per acre. Ginstar is used at rates of 0.0625 to 0.03125 lbs. active ingredient per acre. The organic solvents of Ginstar are believed to desiccate the leaves which prevents the middle lamella of the leaves from fully dissolving, which can prevent the leaves from falling off. Ginstar is not suitable for use in several of the U.S. cotton production areas as a result of the problems of the leaves remaining on the cotton plant. Ginstar is also highly sensitive to the rate used and the variety of the plants where it is applied.
Accordingly, there is a continuing need in the industry for an improved defoliant composition.